The use of manganese dioxide as an active cathode material (depolarizer) in nonaqueous cells is well known. Among the readily available manganese compounds which have been employed as a source of manganese dioxide is manganous nitrate, which is thermally decomposed to produce manganese dioxide. For example Advanced Inorganic Chemistry, F. A. Cotton and G. Wilkinson, published by Interscience--John Wiley and Sons (3rd Ed. 1972) states, at page 852, that manganese dioxide is normally made by heating manganous nitrate hexahydrate in air at a temperature of about 530.degree. C. However, such procedure leads to the production of a highly crystalline beta form of manganese dioxide, or pyrolusite. This material has been used in aqueous batteries of the Leclanche type but in general does not produce as satisfactory results as do other forms of manganese dioxide.
For example, European Pat. No. 27,076 discloses a process for the pyrolysis of manganous nitrate tetrahydrate to form entirely beta type manganese dioxide. More specifically, this process involves heating the Mn(NO.sub.3).sub.2 .multidot.4H.sub.2 O at 150.degree. C., washing the product so obtained first with warm distilled water and subsequently with 1% ammonium hydroxide solution, and then drying the material at a temperature on the order of 400.degree. C. to 450.degree. C. However when moisture resistant manganese dioxide produced using the process of this patent was employed in lithium/non-aqueous cells, such cells did not yield commercially useful efficiencies at temperatures of 21.degree. C. and 35.degree. C. Applicant believes that the reason for the poor performance at these temperatures of such thermally decomposed manganous nitrate is that the beta manganese dioxide produced possesses a highly crystalline form.
Other approaches for the production of electrochemically useful manganese dioxide from manganous nitrate have also been adopted. Among the more useful of these are processes such as that described in U.S. Pat. No. 4,048,027 which involves producing amorphous electrolytic manganese dioxide ("EMD") by the electrolysis of manganous nitrate hexahydrate. In general EMD, which may be heat treated to reduce its water content as is described in British Pat. No. 1,199,426 and U.S. Pat. No. 4,133,856, possesses desirable electrochemical properties for non-aqueous cell usage. However, even heat-treated EMD picks up water so rapidly upon exposure to ambient humidity that, even in a dry room having a relative humidity of from 3-5%, it is difficult to assemble lithium batteries which will maintain capacity. As is well known in the art, moisture present in MnO.sub.2 will react with lithium and/or the nonaqueous electrolyte in a manner which may result in a cell bulging from its initial height. It is therefore an object of this invention to provide a form of manganese dioxide possessing increased resistance to water pickup.
It is also an object of this invention to provide a form of manganese dioxide which possesses a high degree of amorphousness as determined by X-ray diffraction and which is suitable for battery application over a wide range of temperatures.
Further, it is an object of this invention to provide a simple and effective process for the production of a novel form of manganese dioxide from manganous nitrate which is suitable for use in non-aqueous cells.